The present invention relates to the technical field of the treatment of water, especially of wastewater or drinking water. More particularly, the present invention relates to the technical field of the treatment or purification of water in the drinking water or wastewater sector.
More particularly, the present invention relates to a method for treatment or purification of water (untreated water), especially of wastewater or drinking water, preferably for adsorptive removal of inorganic- or organic-based, especially organic-based, contaminants such as trace substances and/or micropollutants.
The present invention further relates to a purification plant, preferably for treatment or purification of water, especially of wastewater or drinking water.
The present invention additionally relates to a countercurrent filter apparatus, especially countercurrent adsorption filter column, which is equally suitable for treatment and purification of water, especially of wastewater or drinking water, and preferably for removal, especially adsorptive removal, of inorganic- or organic-based, especially organic-based, contaminants.
The present invention finally relates to the uses of the purification plant of the invention and of the countercurrent filter apparatus according to the invention, and also of specific adsorption materials in the method according to the invention for treatment or purification of water, especially wastewater or drinking water.
Increasing pollution of the aquatic environment, for example of surface water bodies, but also of groundwater and drinking water, constitutes a major environment-specific problem, especially since water in the form of drinking water is one of the most important and irreplaceable means of sustaining life. More particularly, the introduction of wastewater contaminated with contaminants into water systems and the deployment of contaminated sewage sludge or the like, for example on agricultural land, lead to corresponding contamination and pollution both of surface water and of groundwater.
A particular problem in this context is that of microcontaminants, for which another synonymous term is trace substances or micropollutants. These include not only industrial chemicals and flame retardants but especially also active pharmaceutical ingredients and human pharmaceuticals, such as analgesics, active hormone ingredients or the like, which are secreted in unchanged form or as conjugates or metabolites after chemical conversion in the human organism and, as a result, get into communal wastewater, for example. A further problem is that particular industrial chemicals such as plasticizers, especially bisphenol A, x-ray contrast agents such as amidotrizoic acid and iopamidol, surfactants, such as perfluorinated surfactants, pesticides and the like, since substances of this kind, even in small amounts, have a high toxic potential and/or low biocompatibility. Further examples of microcontaminants generally include antiknock agents such as methyl tert-butyl ether (MTBE).
In addition, what are called dissolved organic compounds or dissolved organic carbons (DOCs) may be cited, which may likewise be present as contaminants in water.
The aforementioned substances or substance classes especially have the feature in common that, even in the event of uptake of very small amounts in the μg or even in the ng range, they can have a considerable influence on the human organism, for example in terms of a hormonal effect, the endocrine disruptor character thereof, the development of resistances or the like.
Human pharmaceuticals, particularly because of the demographic transformation and rising individual life expectancy, with the associated increased consumption of medicaments, will get into the environment via communal wastewater pathways in an even greater amount and number in the future, which is similarly true of veterinary pharmaceuticals because of the general rise in meat consumption with the associated forms of animal keeping.
In addition, pharmacologically active substances which are used in veterinary medicine can similarly get into surface water bodies and into the groundwater, especially as a result of deployment of correspondingly contaminated slurry and subsequent leaching of the agricultural land fertilized thereby by precipitation, such that the corresponding microcontaminants can be flushed into water systems or into the groundwater.
Because of the toxicity, persistence and high bioaccumulation potential of microcontaminants or trace substances and the increasing use of such substances, there is a great need to minimize the introduction or release of microcontaminants into surface water bodies and into the groundwater, and a primary aim in this context should be considered that of effectively treating contaminated wastewater from domestic households, from industry and from medical facilities such as hospitals or other healthcare facilities in order to reduce the level of the corresponding microcontaminants. In this context, the purification of already contaminated drinking water, especially in the waterworks before feeding into the drinking water grid, is also of high relevance, especially since the microcontaminants in question, because of their increasing presence in the aquatic environment, are increasingly present or detectable in drinking water, sometimes in critical amounts.
This is because there may otherwise be unwanted release of the aforementioned substances through the sewage treatment plant effluent into surface water bodies and subsequently also into the groundwater, especially if the microcontaminants are not adequately removed from the original wastewater. Similarly, contaminated wastewater can otherwise get to the end user, which is similarly undesirable.
It can thus be stated in summary that trace substances or microcontaminants, especially in the form of medicaments, but also of industrial and industrial/mechanical origin, are present in wastewater to an increasing degree and can often also get into surface water bodies and into the groundwater as a result of often inadequate treatment or purification of the wastewater, which in turn results in an increased risk of contamination of drinking water, associated with a high endangerment potential for man and the environment.
Against this background, numerous approaches have been pursued in the prior art, which are intended to provide a basis for freeing contaminated water, especially contaminated wastewater or drinking water, of microcontaminants or trace materials, for which purpose plants using various filter apparatuses for wastewater treatment in sewage treatment plants on the one hand and for drinking water treatment on the other hand have been designed, particularly in waterworks. However, the known approaches for water purification do not always lead to the desired success.
Thus, one technical approach for reduction of microcontaminant or trace substance levels involves chemical breakdown of the microcontaminants present in untreated water by means of oxidation processes, the underlying methods generally being referred to as advanced oxidation processes (AOP). These include, for example, an ozone and/or UV treatment of the water to be treated. A disadvantage in the case of these methods, however, is the high energy costs that they often involve, the complex removal of residual ozone in the treated water and the unwanted formation of toxic metabolites or degradation products of the microcontaminants in question.
A further approach to purification of water in the prior art involves using membrane-based filter plants, in which case, for example, the principle of reverse osmosis (RO) and of nanofiltration (NF) and ultrafiltration (UF) is used. However, purifying concepts of this kind are associated with the disadvantage that sometimes complex and costly and also maintenance-intensive filter plants have to be designed and operated, the operation of the corresponding plants being accompanied by high energy costs in some cases. In addition, highly contaminated toxic residues often arise, the disposal of which constitutes a further logistical challenge. Other disadvantages are the sometimes low selectivity and the short operating times and/or service lives of the corresponding filter plants, it being possible for operation to be disrupted for a prolonged period, for example, by (micro-)biological growth on the membranes.
In addition, a further method for reducing the content of microcontaminants in water involves removing the microcontaminants from the water by means of conventional activated carbons. The corresponding concepts together with the technical implementation and the conventional activated carbons used for the purpose, however, are often disadvantageous in that the filter design in the prior art results in low filter capacities and similarly short operating times and/or service lives. Another problem is sometimes (micro-)biological growth in the filter units as such or on the activated carbons used, since this can lead to a reduction in the filter throughput or to a reduction in adsorption capacity.
Moreover, the conventional activated carbons used in the prior art often do not have adequate selectivity and have only low mechanical stability, which can lead to premature abrasion, especially with disadvantageous dust or sludge formation.
More particularly, the prior art often provides for the use of granular adsorptions, but these have a high proportion of binder, and of powdered charcoal, the charcoals used here being based, for example, on hard coal or on charcoals having coconut shells or pitch as starting material. Activated carbons of this kind are often neither mechanically stable nor satisfactory in terms of their adsorption properties, since they often have only a low adsorption capacity and selectivity. A further disadvantage of such activated carbons is that the corresponding industrial filter plants can become blocked as a result of sludge formation, for example on the basis of powdered charcoal or charcoal abrasion, which reduces the throughput capacity and hence the operating time and/or service life.
Moreover, the concepts realized in the prior art involving regeneration of spent activated carbon, i.e. that contaminated with contaminants, is often impossible or can be accomplished only with a high level of cost and inconvenience, especially using steam in a high-temperature process, accompanied by high energy costs and a loss of adsorptions, especially as a result of unwanted burnoff.
The industrial units and plants envisaged for the use of activated carbon are additionally often complex in terms of construction and lead to reduced efficiency in the overall filter assessment. Thus, the activated carbon adsorption stages known in the prior art, which are connected downstream of a mechanical treatment stage and a biological or chemical treatment stage, for example in the context of wastewater treatment, consist of a reaction tank on the one hand and a downstream sedimentation tank on the other hand, the activated carbon being added, especially in pulverulent form, to the reaction tank, and the activated carbon laden with contaminants being removed in the sedimentation tank, often using precipitants or flocculants. Regeneration of the spent charcoal component thus obtained is often impossible, and so the spent activated carbon has to be utilized thermally together with the sewage sludge. The merely thermal final utilization of spent activated carbon also worsens the carbon footprint and hence the overall environmental assessment of the underlying methods.
Plants of this kind for purification of water using conventional activated carbon additionally entail a high space demand, since the corresponding adsorption tanks are designed as open long-life filters which can have a length of more than 10 m. An additional factor is the use of large amounts of activated carbon, since the activated carbons used should be used the long-life filters in a bed having a height of 2 to 3 m, and so a total volume of 200 m3 to 300 m3 of activated carbon per tank is required.
A further approach to adsorptive treatment of water in the prior art involves using closed filter systems having activated carbon in the form of a bed or in a fixed bed. Systems of this kind can also be used, for example, as a downstream purification stage in the context of the treatment of drinking water. As stated above, however, these are filter systems having a closed design in relation to the adsorption material, such that no exchange of the activated carbon component is possible during the operation of the underlying filter plants. In this context, the prior art especially envisages percolation of the water to be purified, especially through a fixed bed filter or a bed of activated carbon based on closed pressure filters. A particular disadvantage here is that systems of this kind are exhausted quickly in terms of the substances to be adsorbed and hence only a limited filter capacity is present. Moreover, it is necessary to renew the entire adsorption material in the filter apparatus after the adsorption material has become exhausted, which results in shutdown of the filter element in question. To compensate for this, complex bypass connections or the use of parallel filter components is required, which makes plants of this kind complex in terms of construction and costly. Another particular disadvantage in this context is the high space demand of such plants.
The closed filter systems envisaged in the prior art, especially pressure filters, are additionally designed such that they have a tubular construction with a generally high diameter and great height, especially since, because of the closed filter arrangement, similarly large volumes of activated carbon are required in the filter system. Pressure filter systems of this kind often have a ratio of height to diameter in the range from about 2 to 3 or less, such that systems of this kind, for this reason too, have a high space demand and sometimes nonoptimal flow conditions within the filter.
Moreover, in the case of such filter concepts, only a limited height of the bed is possible, since, for technical reasons, significant headspace is required within the filter apparatus. More particularly, the closed filter systems of the prior art cited above have only a low height of the adsorption component within the filter and hence only a low adsorption height, the overall result of which is nonoptimal exploitation of the total filter volume. In this context, the prior art pressure filter systems described have a ratio of total column height or filter height to the height of the adsorption material in the filter of 5 to 10 or more.
Moreover, it is a requirement in the aforementioned plants or systems for the water to be purified to be free of suspended materials to a high degree, in order to prevent premature blockage of the filter system. In this regard, another disadvantage in relation to the prior art is that reprocessing or recycling of spent activated carbon is possible only to a very limited degree, one to two recycling runs at best being possible, the effect of which is likewise that large amounts of adsorptions used have to be replaced by new material. More particularly, this is also associated in the prior art with a high loss of activated carbon, which may be up to 25% of the original charge used, the losses in question being caused particularly by dust losses and burnoff. More particularly, efficient reactivation is often impossible.
The above-cited methods and plants using activated carbon as adsorption material allow batchwise exchange of the activated carbon at best, which leads to disadvantageous interruptions of operation and a reduction in efficiency.
Moreover, the aforementioned prior art systems are often inefficient in that satisfactory purification of water to be treated cannot be achieved, especially with regard to problem materials such as dissolved organic carbons (DOCs), perfluorinated surfactants such as perfluorooctanesulfonate (PFOS), antiknock agents such as methyl tert-butyl ether (MTBE), x-ray contrast agents such as iopamidol and amidotrizoic acid.
Furthermore, in relation to the prior art for the plants described therein, there are also unfavorable circulation factors, which represent the ratio of spent activated carbon and that being regenerated to the activated carbon present in the filter system and hence in use for the purposes of purification. In this context, in the prior art, the best conversion factors possible are of 100 or more, especially 200 to 300 or more.
Moreover, such prior art filter systems have relatively low superficial velocities or filtering rates of only 10 m/h at most, particularly in order to enable a certain purification efficiency at all in this way. However, this results in low volumes or amounts of purified water.
Because of the sometimes nonoptimal filter properties of the prior art systems, especially with regard to the closed pressure filters cited above, the result is generally relatively low specific water throughputs before the breakthrough of a trace substance. For example, in the case of prior art systems, the specific water throughput before the breakthrough of the trace substances amidotrizoic acid, given a starting concentration of 290 ng/L in the water for treatment, is about 25 m3/kg of activated carbon.
DE 1 642 396 A1 relates to a method for treatment of wastewater, wherein suspended solids are first removed and wherein the sieved untreated water is treated with a flocculant and the supernatant water is separated from the flocculated material formed and passed through activated carbon beds. The activated carbon beds are back-flushed and regenerated periodically. According to this design, there is thus merely discontinuous or batchwise regeneration of the activated carbon, but this is unfavorable or disadvantageous from a process technology point of view, since the operating times are reduced or the installation of several parallel filter components is necessary as a result. Moreover, the back-flushing in particular is associated with sometimes high losses of adsorption material.
Moreover, DE 2 040 061 A1 relates to a plant for disinfection of wastewater, using disinfectants specific to this purpose. Reduction of microcontaminant levels is not possible on the basis of this design, and the use of disinfectants, moreover, is problematic from an environmental point of view. More particularly, batchwise operation of the plant with back-flushing of the filter element is envisaged, the intention being to remove what is called a return sludge from the apparatus in this way.
Furthermore, German utility model specification DE 88 15 345 U1 relates to a water treatment system, especially for treatment or provision of pollutant-free drinking water, wherein the water treatment system is equipped with a plate module which works by the principle of reverse osmosis. This design is disadvantageous in that the system is of comparatively low selectivity and has to be operated with high energy input, giving contaminated toxic residues.
Moreover, DE 10 2008 041 164 A1 relates to a method for treating water for removal of halide ions by oxidative halogenation of an organic compound added to the water, which is subsequently removed, with conversion of chlorate, iodate and bromate ions remaining in the water to the corresponding halide ions, which is to be followed by another oxidative halogenation. A method of this kind is complex in terms of the process and additionally inefficient in relation to a multitude of microcontaminants.
Finally, EP 1 044 982 A1 relates to a water treatment method which comprises the addition of ozone to untreated water and the filtering of the untreated water using an ozone-resistant membrane, with the option of further treatment of the filtrate with activated carbon or a reverse osmosis membrane. This purification, which is complex in terms of process technology, is sometimes costly and has not been optimized for continuous operation, especially with regard to the use of the activated carbon.